“¡Lo vamos a pasar genial!”
 

Hi. Lo confusing me a lot this week. Why would Lo in this instance be placed before Vamos? How does it change the sentence? If its for emphasis, why not use Nos Vamos?

Thanks!

Pasarlo genial is a set phrase in Spain. It means 'to have a great time'.
Since vamos a is being used to express what is going to happen, the sentence is translated as "We're going to have a great time!"

Another way to say the same thing is ¡Vamos a pasarlo genial! (the pronoun can be suffixed or it can precede the verb (all of the verb includes vamos)).

By the way, outside of Spain the set phrase is pasarla bien. Note that a different pronoun is used, but both phrases mean the same thing.

Thanks, much appreciated!